Precision-engineered surfaces, such as polymeric optical films that include linear prisms or cube-corner prisms to control and direct light, are useful in a variety of applications. For example, cube-corner sheeting can be adapted to reflect light back toward its origin, which makes that retroreflective sheeting useful for road signs or vehicle license plates. Another type of film, having a microstructured adhesive layer to adhere the film to a surface, can be applied with fewer air pockets between the film and the surface, which results in improved appearance and performance.
One way to manufacture such a film is to engrave a metal roll to form a microreplication tool, and then to use that tool to form the film. For example, a molten polymer such as polyester may be extruded onto the microreplication tool and subsequently removed. The film then has one surface that exhibits the opposite structure of the pattern on the microreplication tool. If those patterns are designed appropriately, the film can be used for the purposes noted above, among other things.
U.S. Pat. No. 5,175,030 (Lu et al.) discloses a linear prism or linear groove film that has been used successfully for certain applications. That patent also discloses a microreplication tool or roll on which the linear groove film is produced. The surface of a roll of that type is created by cutting either a succession of adjacent individual grooves or, more commonly, by cutting a single helical groove (commonly referred to as a “thread cut”), into that surface. Although microreplication tools made that way tend to exhibit reasonably precise grooves, the time required to create the tool is considerable. For example, thread-cutting a steel roll using a conventional cutting tool may take weeks of continuous work. If the microreplication tool is used regularly for making film, it may even wear out or otherwise become unusable before a new microreplication tool has been created. As a result, faster methods have been proposed for creating a microreplication tool having linear grooves or other similar structures.
One tool-cutting technique is referred to as “fly-cutting,” in which a diamond-tipped cutting tool is mounted on a rotatable hub. U.S. Patent Application Publication No. 2004/0045419 A1 (Bryan et al.) discloses a fly-cutting device of this type. As the hub is rotated, the cutting tool periodically cuts into the surface of the roll, leaving a groove that approximates an arc of a circle. Successive arcs may overlap each other both in the length-direction of the groove and in the transverse (or lateral) direction, and create grooves that have a scalloped appearance in longitudinal cross-section. These grooves create corresponding scalloped structures in or on a film that is created using the microreplication tool, which may be desirable depending on the desired properties of the film.
In view of these and other conventional tool-cutting devices and methods, it would be beneficial to provide a new fly-cutting head, system, and method that provides for the high-speed creation of a microreplication tool having grooves of a desired topography, and to provide a film or sheeting made using such a tool.